KARACHI, Pakistan_A nationwide strike by Pakistani aircraft engineers protesting pay and work conditions halted flights and left hundreds of passengers stranded across the country Friday, officials said.

The engineers with state-run Pakistan International Airlines went on full strike Friday after launching a work go-slow protest earlier this week, the airline said in a statement.

It led to about 50 flight cancellations - 40 percent of the airline's schedule - in the latest crisis to affect the debt-mired airline, PIA said.

"We are open for discussion, and our senior management is negotiating with them to find a way out," said PIA chairman Zafar Khan.

PIA said that it was continuing talks with the Society of Aircraft Engineers of Pakistan, the body representing the engineers - but that their demands were too high.

Shaukat Jamshed, chairman of the engineers' society, said, "All of our 818 engineers have gone on sick leave, and we will not work over the weekend as well."

PIA was considered one of the best airlines in the developing world in the 1960s and '70s, but in March, the European Union barred most of PIA's planes due to safety concerns. Critics blame the slide in quality and maintenance standards on government interference in the airline's operations.